Aliens are refugees from the Andromeda galaxy, having traveled to the Sol system in a barely-suitable generation ship years ago. They seek the Vaults to improve their lot in life and use the technology and treasures therein to carve out a real home for themselves in the Sol system.
Racially, the Aliens consist of a myriad of unnamed, human sized, Anthropod species, as diverse as the bug life on Earth itself, but all possessing telepathy and some form of coorperative hive mind.